Ice formation may occur at various aerodynamic surfaces of an aircraft when exposed to icing conditions. Ice accretion on an aerodynamic surface can modify the aerodynamic field around it, potentially leading to adverse effects on the aircraft's performance, or may hit and damage other parts of the aircraft after shedding.
In order to prevent or reduce ice formation, several ice protection devices and methods have been developed. There are two different approaches when dealing with ice protection systems: allowing ice formation to a certain extent and removing it afterwards (de-icing) or avoiding any ice formation from occurring in the first place (anti-icing).
The most common anti-icing systems are those based on heating the inner face of the aerodynamic surface with hot air bled from the engine compressor, having the external surface heated by conduction through the material. These types of systems have a low overall efficiency. In modern aircraft, where the use of composite materials is increasing, this system proves to be of very low efficiency when heating aerodynamic surfaces made of carbon fiber reinforced polymer (CFRP) due to the material's poor thermal conductivity. Moreover, CFRP laminates are limited in temperature to values much lower than those for metallic materials.
Alternatives to ice protection of aircraft aerodynamic surfaces exist. Systems can be based on the modification of external surface properties to avoid ice formation, either on metallic parts by modification of the nanometric rugosity or by depositing different products impregnated in adhesives. Another group uses direct heating of aerodynamic surfaces by means of air systems or similar, but a great part of the new contributions use variants of heating by Joule effect combined with more or less conventional systems, with AC or DC current depending on requirements, by means of electrothermal effects or even with the use of carbon nanotubes.
Another alternative is to heat the aerodynamic surfaces by electromagnetic induction: eddy currents are formed in electrically conductive materials which then heat the material by Joule effect. This method has been studied for its use with metallic parts of turbines, as well as with composite materials.
The issue of using electromagnetic induction is that, in order to generate the eddy currents, a thin layer of an electrically conductive material (e.g., metal) is needed, which is not a feature of laminates made of CFRP. Moreover, a specific winding distribution is needed to induce the currents on the conductive layer in such a way that they are uniformly spread and the heating target is reached in every area.
The aim of ice protection systems based on heating is to increase the temperature of the aerodynamic surface's outer layer to a temperature that impedes ice formation.
When trying to heat CFRP structures by electromagnetic induction, the poor electrical properties of the carbon fibers and the polymer matrix do not allow for strong eddy currents to form inside the material; hence, little or no heat at all is generated in the material.